The particles of fibrous basic magnesium sulfate [MgSO4.5Mg(OH)2.3H2O] are utilized as reinforcing material for paper, resin and rubber, or raw material for manufacturing filters. There have been known the following preparation processes for producing the fibrous basic magnesium sulfate particles.
JP-A-56-149318 (Patent publication 1) describes a process for producing fibrous basic magnesium sulfate particles by hydrothermal reaction. In more detail, the publication discloses a process comprising the steps of dispersing magnesium hydroxide or magnesium oxide in an aqueous magnesium sulfate in an amount of 25 wt. % or less and subjecting the dispersion to hydrothermal reaction at a temperature of 100 to 300° C., preferably 120 to 300° C.
JP-A-3-122012 (Patent publication 2) discloses a process for producing fibrous basic magnesium sulfate particles utilizing no hydrothermal reaction. In more detail, the process comprises the steps of heating an aqueous dispersion which is prepared by dispersing a magnesium oxide powder in an aqueous sulfate-containing solution preferably at an ordinary pressure and a temperature of 60° C. or higher, but lower than the boiling point, to produce a massive basic magnesium sulfate, and disintegrating the massive product under strong shearing force.
It is required to utilize a pressure-resistant vessel such as autoclave for performing the process for producing fibrous basic magnesium sulfate particles by hydrothermal reaction (which is disclosed in Patent publication 1). Therefore, it is difficult to continuously produce the fibrous basic magnesium sulfate particles.
The process of Patent publication 2 is advantageous in the non-use of hydrothermal reaction. However, it is required to perform an additional step for disintegrating the massive basic magnesium sulfate.